In this study, it is carried out to analysis of the bolt pretension of the stress-laminated timber. Bolt pretension of stress-laminated timber was decreased by time. The loss of force is caused by moisture content, shrinkage of wood. After re-stressing the stress-laminated timber, the rate of force decrement was slowed significantly. To use of stress-laminated timber for the service, it is necessary to make an accurate estimate of force. It is clear that is different between actual value and predicted value changes by existing model for bolt pretension of stress-laminated timber. Accordingly, considering the time and the external environment, the development of prediction model is needed.